Treatment method for reducing steam emptying during start-up of ammonia synthesis device

Abstract

The invention discloses a treatment method for reducing steam emptying during start-up of an ammonia synthesis device. Comprising an ammonia synthesis tower, a medium-pressure waste boiler, a steam heater, a medium-low temperature and pressure reducer, a 3.8 MPa steam pipe network, a 0.5 MPa steam pipe network, a conversion device, a compressor low-pressure cylinder, a compressor medium-pressure cylinder, a compressor high-pressure cylinder, a heat exchanger, a boiler water heater, a low-pressure waste boiler, a first water cooler, a second water cooler, a cold exchanger, a primary ammonia cooler, a secondary ammonia cooler and an ammonia separator. By arranging the medium-low temperature and pressure reducer and the matched steam switching system, high-efficiency utilization of steam in the start-up stage is realized in a manner of reducing the temperature and the pressure of low-temperature 3.8 MPa saturated steam to 0.5 MPa steam and recycling the steam, so that the problem of energy waste caused by forced emptying due to insufficient steam temperature in the background technology is solved, and the energy consumption is reduced. And meanwhile, noise pollution of a production field is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of ammonia synthesis production, and particularly to a method for reducing steam venting during the startup of an ammonia synthesis device. Background Art

[0002] Fresh gas with a pressure of 3.0 MPa and a temperature of 30 °C coming from purification and recycle gas returning from the synthesis loop are pressurized to 14.1 MPa(A) by a compressor. After being heated through a heat exchanger, they are sent into the ammonia synthesis tower. The synthesis gas reacts to produce NH3 under the action of high temperature, high pressure, and a catalyst. Then, it is cooled and condensed through heat exchange in a steam superheater, a medium-pressure waste heat boiler, a boiler feed water heater, a low-pressure waste heat boiler, a heat exchanger, a water cooler, a cold exchanger, a first-stage ammonia cooler, and a second-stage ammonia cooler. Liquid ammonia is separated by an ammonia separator, and the product liquid ammonia is sent out of the battery limit. The unreacted gas returns to the recycle section of the synthesis gas compressor and merges with the fresh gas. After increasing the pressure, it continues to enter the synthesis tower for reaction.

[0003] Currently, during the startup stage, due to the relatively low temperature of the ammonia synthesis tower, the 3.8 MPa saturated steam produced by the medium-pressure waste heat boiler and the 3.8 MPa saturated steam sent from the conversion device, after being heated by a steam heater, the temperature of the 3.8 MPa superheated steam is lower than 360 °C and cannot be merged into the 3.8 MPa superheated steam pipe network, resulting in this part of the steam being forced to be vented; this not only causes energy waste but also increases the noise at the production site. Therefore, it is very necessary and meaningful to design a more efficient method for not venting the 3.8 MPa superheated steam during the startup stage of the ammonia synthesis device. Summary of the Invention

[0004] In view of the above problems, the present invention provides a method for reducing steam venting during the startup of an ammonia synthesis device. By using the temperature and pressure reduction technology, the unusable 3.8 MPa saturated steam is converted into 0.5 MPa steam for use by other devices, and then switched to the 3.8 MPa steam pipe network after the steam temperature reaches the standard, thereby reducing energy waste and noise pollution.

[0005] The technical solution of the present invention is as follows:

[0006] Regarding the method for reducing steam venting during the startup of an ammonia synthesis device, it includes an ammonia synthesis tower, a medium-pressure waste heat boiler, a steam heater, a medium-low temperature and pressure reducer, a 3.8 MPa steam pipe network, a 0.5 MPa steam pipe network, a conversion device, a low-pressure cylinder of the compressor, a medium-pressure cylinder of the compressor, a high-pressure cylinder of the compressor, a heat exchanger, a boiler water heater, a low-pressure waste heat boiler, a first water cooler, a second water cooler, a cold exchanger, a first-stage ammonia cooler, a second-stage ammonia cooler, and an ammonia separator.

[0007] The above treatment method steps are as follows:

[0008] S1. Low-temperature steam desuperheating and pressure reduction treatment: In the initial stage of startup, the temperature of the catalyst in the ammonia synthesis tower is relatively low, about 200 °C. The 3.8 MPa saturated steam produced by the medium-pressure waste heat boiler and the conversion unit is still below 360 °C after being heated by the steam heater and cannot be incorporated into the 3.8 MPa steam pipe network. At this time, the steam is reduced in pressure to 0.5 MPa and cooled to 180 - 210 °C through the medium-low desuperheater and pressure reducer to meet the requirements of the low-pressure pipe network for use.

[0009] S2. Steam is transported to the low-pressure pipe network: The reduced-pressure steam is transported through the 0.5 MPa steam pipe network to other devices for use, avoiding waste by venting.

[0010] S3. High-temperature steam is switched and connected to the grid: Continuously monitor the temperature at the outlet of the steam heater. After the temperature of the 3.8 MPa superheated steam exceeds 360 °C, close the inlet valve of the medium-low desuperheater and pressure reducer, and open the 3.8 MPa superheated steam outgoing valve II to switch the steam to the 3.8 MPa steam pipe network.

[0011] In a further technical solution, the desuperheating water of the medium-low desuperheater and pressure reducer is supplied through the 2.5 MPa boiler water pipeline and the 2.5 MPa desuperheating water valve to ensure the stability and controllability of the desuperheating process.

[0012] In a further technical solution, the sequence of putting into use and withdrawing the medium-low desuperheater and pressure reducer is opposite: When putting into use, first pass the steam and then the desuperheating water; when withdrawing, first stop the desuperheating water and then the steam, preventing the occurrence of water hammer phenomenon and solving the problem of equipment damage caused by improper operation in the prior art.

[0013] In a further technical solution, the steam temperature of the 0.5 MPa steam pipe network is controlled within the range of 180 - 210 °C to ensure that the steam quality meets the requirements of downstream devices.

[0014] In a further technical solution, the 3.8 MPa saturated steam is sent to the steam heater after being converged by the medium-pressure waste heat boiler and the conversion unit through the 3.8 MPa saturated steam pipeline, realizing the centralized treatment and utilization of steam.

[0015] In a further technical solution, the heating-up time of the ammonia synthesis tower is 6 hours, and the total startup time is 20 hours. During this period, 30 t / h of 0.5 MPa steam can be recovered, significantly reducing energy waste.

[0016] In a further technical solution, the compressor includes a low-pressure cylinder, a medium-pressure cylinder, and a high-pressure cylinder. The hydrogen-nitrogen gas enters the ammonia synthesis tower after being compressed through each stage in turn to ensure that the synthesis gas reaches the pressure and temperature conditions required for the reaction.

[0017] In a further technical solution, the syngas, after reacting in the ammonia synthesis tower, successively passes through a steam heater, a medium-pressure waste heat boiler, a boiler water heater, a low-pressure waste heat boiler, a heat exchanger, a first water cooler, a second water cooler, a cold exchanger, a primary ammonia cooler and a secondary ammonia cooler for cooling and heat recovery, realizing the cascade utilization of energy.

[0018] In a further technical solution, the hydrogen-nitrogen gas separated by the ammonia separator returns to the high-pressure cylinder of the compressor for recycling after recovering cold energy through the cold exchanger, improving the utilization rate of the raw material gas.

[0019] In a further technical solution, 30 t / h of 0.5 MPa steam can be recovered during the start-up stage. Calculated at 145 yuan per ton of steam, the cost is saved by 87,000 yuan, and the economic benefit is remarkable.

[0020] The beneficial effects of the present invention are as follows:

[0021] 1. By setting up a medium-low temperature and pressure reducing valve and a supporting steam switching system, the low-temperature 3.8 MPa saturated steam is cooled and depressurized to 0.5 MPa steam for recycling, realizing the efficient utilization of steam during the start-up stage, thus solving the problem of energy waste caused by forced venting due to insufficient steam temperature in the background technology, and at the same time reducing the noise pollution at the production site;

[0022] 2. By setting up a 2.5 MPa desuperheating water system and a sequence control process, the desuperheating and depressurization process is precisely controlled and the safe operation mode of "first injecting steam and then injecting desuperheating water" is adopted, realizing the stable adjustment of steam parameters and the safe operation of equipment, thus solving the problems of unstable steam parameters and potential operation safety hazards in the background technology;

[0023] 3. By setting up a multi-stage energy recovery system, the depressurized steam is supplied to other devices for use and the recycle gas of the ammonia synthesis device is recycled, realizing the cascade utilization of energy and the efficient recycling of the raw material gas, thus solving the problems of low energy utilization rate and raw material waste, enabling 30 t / h of steam to be recovered during the start-up stage and saving costs. Description of the Drawings

[0024] Figure 1 is the overall process schematic diagram of the embodiment of the present invention.

[0025] Description of the Reference Numerals in the Drawings

[0026] 1. 0.5 MPa steam pipe network; 2. Outlet valve of the medium and low temperature desuperheater; 3. Medium and low temperature desuperheater; 4. Inlet valve of the medium and low temperature desuperheater; 5. Outlet valve II of 3.8 MPa superheated steam; 6. 3.8 MPa steam pipe network; 7. 3.8 MPa steam vent pipeline I; 8. 3.8 MPa steam vent valve; 9. 3.8 MPa steam pipeline to the sky II; 10. Pipeline to the ammonia synthesis tower; 11. Ammonia synthesis tower; 12. Pipeline for syngas to enter the steam superheater; 13. Pipeline for syngas to enter the medium pressure waste heat boiler; 14. Outlet valve of 3.8 MPa saturated steam; 15. Steam heater; 16. Outlet valve I of 3.8 MPa superheated steam; 17. Medium pressure waste heat boiler; 18. 3.8 MPa saturated steam pipeline; 19. 2.5 MPa desuperheated water pipeline; 20. Conversion 3.8 MPa saturated steam valve; 21. Conversion 3.8 MPa saturated steam pipeline; 22. Outlet valve of 0.5 MPa steam; 23. Low pressure waste heat boiler; 24. 2.5 MPa desuperheated water valve; 25. 2.5 MPa boiler water pipeline; 26. Inlet valve of low pressure waste heat boiler water; 27. Pipeline for syngas to enter the heat exchanger; 28. Pipeline for syngas to enter the low pressure waste heat boiler; 29. Boiler water heater; 30. 5.0 MPa boiler water valve; 31. 5.0 MPa boiler water pipeline; 32. 5.0 MPa high temperature boiler water pipeline; 33. Pipeline for syngas to enter the boiler water heater; 34. Heat exchanger; 35. Pipeline for syngas to enter the first water cooler; 36. Pipeline for hydrogen-nitrogen gas to enter the heat exchanger; 37. Pipeline for syngas to enter the cold exchanger; 38. Second water cooler; 39. First water cooler; 40. Pipeline for syngas to enter the second water cooler; 41. Pipeline for circulating gas to enter the cold exchanger; 42. Pipeline for syngas to enter the first stage ammonia cooler; 43. First stage ammonia cooler; 44. Pipeline for syngas to enter the second stage ammonia cooler; 45. Second stage ammonia cooler; 46. Pipeline for syngas to enter the ammonia separator; 47. Ammonia separator; 48. Steam turbine; 49. Valve for circulating gas to enter the high pressure cylinder of the compressor; 50. Pipeline for circulating gas to enter the high pressure cylinder of the compressor; 51. Cold exchanger; 52. Pipeline from the low pressure cylinder to the medium pressure cylinder; 53. Pipeline for ammonia synthesis make-up gas; 54. Valve for ammonia synthesis make-up gas; 55. Low pressure cylinder of the compressor; 56. Medium pressure cylinder of the compressor; 57. High pressure cylinder of the compressor; 58. Pipeline from the medium pressure cylinder to the high pressure cylinder; 59. Outlet valve of the compressor. Detailed implementation manners

[0027] The embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0028] Embodiment:

[0029] As Figure 1As shown in the figure, the treatment method for reducing steam venting during the start-up of an ammonia synthesis plant includes an ammonia synthesis tower 11, a medium-pressure waste heat boiler 17, a steam heater 15, medium-low temperature desuperheating and pressure reducing valves 3, a 3.8 MPa steam pipeline network 6, a 0.5 MPa steam pipeline network 1, a conversion unit, a low-pressure cylinder 31 of a compressor, a medium-pressure cylinder 56 of a compressor, a high-pressure cylinder 57 of a compressor, a heat exchanger 34, a boiler water heater 29, a low-pressure waste heat boiler 23, a first water cooler 39, a second water cooler 38, a cold exchanger 51, a first-stage ammonia cooler 43, a second-stage ammonia cooler 45, and an ammonia separator 47. The desuperheating water of the medium-low temperature desuperheating and pressure reducing valve 3 is supplied through a 2.5 MPa boiler water pipeline 25 and a 2.5 MPa desuperheating water valve 24. When the medium-low temperature desuperheating and pressure reducing valve 3 is put into use and withdrawn, the sequence is opposite. When putting it into use, steam is put in first and then desuperheating water. When withdrawing, desuperheating water is withdrawn first and then steam. The steam temperature of the 0.5 MPa steam pipeline network 1 is controlled within the range of 180 - 210 °C. The 3.8 MPa saturated steam from the medium-pressure waste heat boiler 17 and the conversion unit is sent to the steam heater 15 after converging through a 3.8 MPa saturated steam pipeline 18.

[0030] The treatment method steps are as follows:

[0031] Steam desuperheating and pressure reducing stage: In the initial stage of start-up, when the catalyst temperature in the ammonia synthesis tower 11 is lower than 200 °C, the 3.8 MPa saturated steam generated by the medium-pressure waste heat boiler 17 and the conversion unit is still lower than 360 °C after being heated by the steam heater 15. At this time, open the external delivery valve 2 and the inlet valve 4 of the medium-low temperature desuperheating and pressure reducing valve, and use the desuperheating water provided by the 2.5 MPa boiler water pipeline 25 to reduce the pressure of the steam to 0.5 MPa, and control the temperature within the range of 180 - 210 °C, and then send it into the 0.5 MPa steam pipeline network 1. Operate strictly in accordance with the sequence of "putting in steam first and then desuperheating water" to prevent water hammer phenomenon, avoid waste of steam venting, realize energy recovery and utilization, and at the same time reduce noise pollution.

[0032] The heating-up time of the ammonia synthesis tower 11 is 6 hours, and the total start-up time is 20 hours.

[0033] Steam pipeline network switching stage: Continuously monitor the temperature at the outlet of the steam heater 15. When the temperature of the 3.8 MPa superheated steam exceeds 360 °C, first close the desuperheating water valve 24, then close the inlet valve 4 of the medium-low temperature desuperheating and pressure reducing valve, and finally open the 3.8 MPa superheated steam external delivery valve II 5 to merge the steam into the 3.8 MPa steam pipeline network 6. The switching process needs to be operated smoothly to avoid pressure fluctuations, realize the smooth transition of the steam system, and ensure the stable operation of downstream devices.

[0034] The compressor includes a low-pressure cylinder 31, a medium-pressure cylinder 56, and a high-pressure cylinder 57. Hydrogen-nitrogen gas enters the ammonia synthesis tower 11 after being compressed by each stage in sequence. After the synthesis gas reacts in the ammonia synthesis tower 11, it successively passes through a steam heater 15, a medium-pressure waste heat boiler 17, a boiler feed water heater 29, a low-pressure waste heat boiler 23, a heat exchanger 34, a first water cooler 39, a second water cooler 38, a cold exchanger 51, a primary ammonia cooler 43, and a secondary ammonia cooler 45 for cooling and heat recovery. The hydrogen-nitrogen gas separated by the ammonia separator 47 returns to the high-pressure cylinder 57 of the compressor for recycling after recovering cold energy through the cold exchanger 51.

[0035] Gas compression cycle stage: Fresh gas and recycle gas are successively pressurized to 14.5 MPa through the low-pressure cylinder 31, medium-pressure cylinder 56, and high-pressure cylinder 57 of the compressor, enter the ammonia synthesis tower 11 for reaction after being heated up by the heat exchanger 34. After the reaction, the gas is successively cooled by each heat exchange device. After being separated by the ammonia separator 47, the unreacted gas returns to the high-pressure cylinder 57 of the compressor for recycling after recovering cold energy through the cold exchanger 51. Strictly control the compression ratio and temperature parameters of each stage to improve the utilization rate of the raw material gas and achieve cascaded energy utilization.

[0036] During the startup stage, 0.5 MPa steam can be recovered at a rate of 30 t / h.

[0037] Heat recovery and utilization stage: The heat of the synthesis reaction generates 3.8 MPa saturated steam through the medium-pressure waste heat boiler 17. The boiler feed water heater 29 heats the demineralized water to 220 °C, and the low-pressure waste heat boiler 23 recovers the low-temperature waste heat. During the startup stage, 0.5 MPa steam can be recovered at a rate of 30 t / h. Optimize the operating parameters of the heat exchange equipment to maximize the recovery of the reaction heat, significantly reduce the energy consumption, and save the production cost.

[0038] During the whole process, monitor the steam temperature and pressure parameters throughout. According to the temperature rise situation of the ammonia synthesis tower 11, about 6 hours, and the total startup time of 20 hours, adjust the operating parameters in a timely manner. Through the combination of each process, the present invention realizes the efficient recovery and utilization of steam energy during the startup process of the ammonia synthesis device, solves the problems of energy waste and environmental pollution caused by steam venting in the traditional process, and improves the economy and safety of the entire production system at the same time.

[0039] The above embodiments only represent the specific implementation manners of the present invention, and the description is relatively specific and detailed, but it should not be construed as a limitation to the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. Method for reducing steam venting during the startup of an ammonia synthesis unit, including an ammonia synthesis tower (11), a medium-pressure waste heat boiler (17), a steam heater (15), a medium-low temperature desuperheating and pressure reducing valve (3), a 3.8 MPa steam pipe network (6), a 0.5 MPa steam pipe network (1), a conversion unit, a low-pressure cylinder of a compressor (31), a medium-pressure cylinder of a compressor (56), a high-pressure cylinder of a compressor (57), a heat exchanger (34), a boiler water heater (29), a low-pressure waste heat boiler (23), a first water cooler (39), a second water cooler (38), a cold exchanger (51), a first-stage ammonia cooler (43), a second-stage ammonia cooler (45), and an ammonia separator (47); The treatment method steps are as follows: S1. Low-temperature steam desuperheating and pressure reducing treatment: In the initial stage of startup, for the situation where the catalyst temperature in the ammonia synthesis tower (11) is low, the 3.8 MPa saturated steam produced by the medium-pressure waste heat boiler (17) and the conversion unit is depressurized and cooled by a desuperheating and pressure reducing valve. S2. Steam is transported to the low-pressure pipe network: The steam after desuperheating and pressure reducing is transported to the 0.5 MPa steam common pipe network (1) for use by other devices. S3. High-temperature steam is switched and connected to the grid: Continuously monitor the steam temperature at the outlet of the steam heater (15). When the temperature of the 3.8 MPa superheated steam exceeds 360 °C, switch the transportation path and send the steam into the 3.8 MPa steam common pipe network (6).

2. The method for reducing steam venting during the startup of an ammonia synthesis unit according to claim 1, wherein The desuperheating water of the medium-low temperature desuperheating and pressure reducing valve (3) is supplied through a 2.5 MPa boiler water pipeline (25) and a 2.5 MPa desuperheating water valve (24).

3. The method for reducing steam venting during the start-up of an ammonia synthesis plant according to claim 1, characterized in that, When the medium-low temperature desuperheating and pressure reducing valve (3) is adopted and withdrawn, the order is opposite. When adopted, steam is input first and then desuperheating water. When withdrawn, desuperheating water is withdrawn first and then steam.

4. The method for reducing steam venting during the start-up of an ammonia synthesis unit according to claim 1, characterized in that, The steam temperature of the 0.5 MPa steam pipe network (1) is controlled within the range of 180 - 210 °C.

5. The method for reducing steam venting during the start-up of an ammonia synthesis unit according to claim 1, characterized in that, The 3.8 MPa saturated steam is sent from the medium-pressure waste heat boiler (17) and the conversion unit to the steam heater (15) after converging through a 3.8 MPa saturated steam pipeline (18).

6. The method for reducing steam venting during the startup of an ammonia synthesis unit according to claim 1, characterized in that, The heating-up time of the ammonia synthesis tower (11) is 6 hours, and the total startup time is 20 hours.

7. The method for reducing steam venting during the start-up of an ammonia synthesis unit according to claim 1, characterized in that, The compressor includes a low-pressure cylinder (31), a medium-pressure cylinder (56), and a high-pressure cylinder (57). Hydrogen-nitrogen gas enters the ammonia synthesis tower (11) after being compressed by each stage in sequence.

8. The method for reducing steam venting during the startup of an ammonia synthesis unit according to claim 1, characterized in that, After the syngas reacts in the ammonia synthesis tower (11), it is cooled and heat is recovered through a steam heater (15), a medium-pressure waste heat boiler (17), a boiler water heater (29), a low-pressure waste heat boiler (23), a heat exchanger (34), a first water cooler (39), a second water cooler (38), a cold exchanger (51), a first-stage ammonia cooler (43), and a second-stage ammonia cooler (45) in sequence.

9. The method for reducing steam venting during the start-up of an ammonia synthesis unit according to claim 1, characterized in that, The hydrogen-nitrogen gas separated by the ammonia separator (47) returns to the high-pressure cylinder (57) of the compressor for recycling after recovering cold energy through the cold exchanger (51).

10. The method for reducing steam venting during the start-up of an ammonia synthesis unit according to claims 1-8, characterized in that, During the startup stage, 30 t / h of 0.5 MPa steam can be recovered.

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